Resistivity tapered wideband high frequency antennas for tactical communications

The authors describe theoretical and experimental investigations on high-frequency monopole antennas for ground terminals and transmission-line type antennas for helicopters where tapered resistivity loading has been used to achieve a traveling wave current distribution on the antenna. The tapered resistivity profiles used in these antennas are modified versions of the theoretical model first proposed by T.T. Wu and R.W.P. King (1965). Various types of optimized resistivity taper profiles that allow the best tradeoff between efficiency and bandwidth have been considered. Antenna characteristics such as input impedance, efficiency, radiation pattern and current distribution have been calculated using the NEC-3 method of moments code. Wideband HF antennas have been designed for the UH-1D and the HH-60J helicopters using suitable wire grid models to represent the fuselage of these helicopters. Prototype models of monopole antennas and scale model helicopter antennas have been built and tested and are in good qualitative agreement with theoretical predictions